Generally, wiring technology refers to a technology for realizing interconnections, power supplying routes, and signal transmission routes of transistors in an integrated circuit (IC).
As design rules have been reduced due to the higher integration of semiconductor devices, memory cells have been stacked. Therefore, interconnection lines for electrically connecting between cells are formed in a multi-layer structure in order to freely perform wiring design and easily set resistance and current capacities of interconnection lines.
Conventionally, aluminum (Al) has been widely used as a line material. However, line resistance and contact resistance have been increased by decrease of line widths according to a trend of higher integration. Therefore, research on copper (Cu) lines is actively being undertaken for that reason and to cope with a problem of electromigration (EM). Copper has a lower resistivity than that of aluminum by about 62%, and copper has better strength against electromigration. Therefore, better reliability may be obtained from copper lines, especially for a semiconductor device of high integration and high speed.
In addition, an insulating layer having a low dielectric constant (low-k) of less than 3.0 is used for an insulating layer between interconnection lines in order to decrease a parasitic capacitance therein.
On the other hand, it is very difficult to pattern copper because copper is difficult to dry-etch in comparison with aluminum, and an insulating layer having a low-k has a drawback in that a gap-filling characteristic is poor.
Accordingly, a damascene process for simultaneously forming a contact and an interconnection line has recently been used to solve such a problem. The damascene process is carried out as follows. Firstly, an insulating layer having a low-k is formed, and then a damascene structure including a via hole and a line-shaped trench is formed. Next, the damascene structure is filled with a copper layer by electrolysis of a copper seed layer formed in the damascene structure. Finally, an overflowing portion of the copper layer is removed by chemical mechanical polishing (CMP).
In addition, a damascene structure is formed by performing one among a via-first, trench-first, or self-align scheme. The via-first scheme is a process to form a line-shaped trench on an upper part of a via hole after firstly forming a via hole by etching an insulating layer. On the other hand, the trench-first scheme is a process to firstly form a trench on an insulating layer before forming a via hole. The self-align scheme is a process to form a via hole and a trench simultaneously.
However, when an electroplating method is performed in order to fill a damascene structure with a copper layer after forming a copper seed layer as described above, seams in the copper layer may occur in an inner part of the damascene structure, particularly at a boundary region between the via hole and the trench, because the copper layer is deposited at a different speed according to an aspect ratio of the damascene structure.
Such seams deteriorate strength against electromigration. Moreover, such seams deteriorate characteristics and reliability of a device because they are opened during a CMP process so as to induce critical defects of a device.
The above information disclosed in this section is only for enhancement of understanding of the background of the disclosure and, therefore, it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.
To clarify multiple layers and regions, the thickness of the layers are enlarged in the drawings. Wherever possible, the same reference numbers will be used throughout the drawing(s) and accompanying written description to refer to the same or like parts. As used in this patent, stating that any part (e.g., a layer, film, area, or plate) is in any way positioned on (e.g., positioned on, located on, disposed on, or formed on, etc.) another part, means that the referenced part is either in contact with the other part, or that the referenced part is above the other part with one or more intermediate part(s) located therebetween. Stating that any part is in contact with another part means that there is no intermediate part between the two parts.